Organ preservation techniques typically involve hypothermic storage of the organ in a chemical perfusate solution on ice. In the case of a heart, it is typically arrested, and cooled with a cardioplegic solution until it reaches a hypothermic, non-functioning state and then is stored in or perfused with a cold preservation solution. These techniques utilize a variety of cardioplegic and cold preservation solutions, none of which sufficiently protect the heart from myocardial damage resulting from ischemia. Such injuries are particularly undesirable when an organ, such as a heart, is intended to be transplanted from a donor into a recipient. In addition to myocardial damage resulting from ischemia, reperfusion of a heart may exacerbate the myocardial injury and may cause coronary vascular endothelial and smooth muscle injury, which may lead to coronary vasomotor dysfunction.
Using conventional approaches, such injuries increase as a function of the length of time an organ is maintained ex-vivo. For example, in the case of a heart, typically it may be maintained ex-vivo for only 4-6 hours before it becomes unusable for transplantation. This relatively brief time period limits the number of recipients who can be reached from a given donor site, thereby restricting the recipient pool for a harvested heart. Even within the 4-6 hour time limit, the heart may nevertheless be significantly damaged. A significant issue is that there may not be any apparent indication of the damage. Compounding the effects of cold ischemia, current cold preservation techniques preclude the ability to evaluate and assess an organ ex-vivo. Because of this, less-than-optimal organs may be transplanted, resulting in post-transplant organ dysfunction or other injuries. Thus, it would be desirable to develop techniques that can extend the time during which an organ can be preserved in a healthy state ex-vivo and that can provide an environment within which an organ can be evaluated ex-vivo. Such techniques would improve transplant outcomes and enlarge potential donor and recipient pools.
Effective maintenance of an ex-vivo organ would also provide numerous other benefits. For instance, ex-vivo maintenance of an organ in a living, functioning, near-physiologic state would permit more careful monitoring and evaluation of the harvested organ. This would in turn allow earlier detection and potential repair of defects in the harvested organ, further improving transplantat outcomes. The ability to perform simple repairs on the organ would also allow many organs with minor defects to be saved, whereas current transplantation techniques require them to be discarded.
In addition, more effective matching between the organ and a particular recipient may be achieved, further reducing the likelihood of eventual organ rejection. Current transplantation techniques rely mainly on matching donor and recipient blood types, which by itself is not a foolproof indicator of whether or not the organ will be rejected by the recipient. A more complete test for organ compatibility is a Human Leukocyte Antigen (HLA) matching test, but current cold ischemic organ preservation approaches preclude the use of this test, which can often require twelve hours or more to complete.
Prolonged and reliable ex-vivo organ care would also provide benefits outside the context of organ transplantation. For example, a patient's body, as a whole, can typically tolerate much lower levels of chemo-, bio- and radiation therapy than many particular organs. An ex-vivo organ care system would permit an organ to be removed from the body and treated in isolation, reducing the risk of damage to other parts of the body.
Electrodes are used in some heart perfusion systems to measure the electrical activity of the explanted heart and to deliver defibrillation energy. There are a number of issues associated with these electrodes, such as their size, which makes them difficult to position and may cause them to come in contact with each other resulting in erroneous signals, particularly on smaller hearts. In addition, these electrodes require wetting with blood to establish electrical contact with the heart, have a tendency to move around due to vibration during transport and beating of the heart resulting in a loss of signal fidelity, have biocompatibility issues, and are incompatible with the sterilization method (ETO) used to sterilize components of the perfusion systems.